Thermoplastic polyurethane materials are some of the most commonly used biomaterial polymer for various medical applications. Some thermoplastic polyurethane materials are stiff and their flexibility may not be controllable. This limits their use in many types of polyurethane medical applications, especially for long-term medical uses. In some cases, these materials are not able to maintain their original stiffness or other physical property and their physical properties change too quickly.
For medication infusion or injection, an invasive medical device is typically used to create a fluid channel from a medication reservoir to the patient, usually to vascular vessels or subcutaneous tissue. To ensure success of insertion to the body tissue of a target area, the entry portion of the device needs to be stiff enough for minimum pain. Intravascular catheters, for example, are currently utilized in a wide variety of minimally invasive medical procedures. Generally, an intravascular catheter allows a clinician to remotely perform a medical procedure by inserting the catheter into the patient's vascular system. Typically, the practice is to insert a flexible catheter tube into a vein and leave the catheter tube in such a position for purposes such as periodically administering fluids, transfusions and medication, collecting of blood samples, and the like. The catheter tube may remain in place for days or weeks at a time. After the distal portion of the catheter tube has entered the patient's vascular system, the clinician may advance the distal tip forward by applying longitudinal forces to the proximal portion of the catheter and bend force to the catheter tube body. For the catheter tubing to effectively communicate these longitudinal forces, it is desirable that the catheter tube has a high level of pushability, which can be translated to a material property of high stiffness of catheter tube. In some countries, nursing practices prior to insertion of IV catheter include pre-priming the IV catheters in 25° C. (or ambient) saline, which can cause the tubing to soften such that insertion becomes difficult. Once reaching the tissue, such as a blood vessel, the part of the device that remains in the tissue needs to be soft enough to minimize potential complications, such as mechanical phlebitis, and improve patient comfort. In some instances, a catheter may cause phlebitis, which is an inflammation of a vein, due to local trauma to the vein in which the catheter is inserted. Harder catheters in the vein can be more likely to cause such trauma.
There remains a need for polyurethanes for catheter manufacture that are stiff under ambient conditions for catheter insertion but which becomes soft and pliable for positioning and indwelling only upon exposure to more than one in vivo stimuli.